Tool Compensation

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1. Tool Length Offsets

1.1. Touch Off

Using the Touch Off Screen in the AXIS interface you can update the
tool table automatically.

Typical steps for updating the tool table:

After homing load a tool with Tn M6 where n is the tool number.

Move tool to an established point using a gauge or take a test cut and
measure.

Click the "Touch Off" button in the Manual Control tab (or hit the
End button on your keyboard).

Select Tool Table in the Coordinate System drop down box.

Enter the gauge or measured dimension and select OK.

The Tool Table will be changed with the correct Z length to make the
DRO display the correct Z position and a G43 command will be issued so
the new tool Z length will be in effect. Tool table touch off is only
available when a tool is loaded with Tn M6.

Figure 1. Touch Off Tool Table

1.2. Using G10 L1/L10/L11

The G10 L1/L10/L11 commands can be used to set tool table offsets:

G10 L1 Pn - Set offset(s) to a value. Current position irrelevant.
(see G10 L1 for details)

G10 L10 Pn - Set offset(s) so current position w/ fixture 1-8 becomes a value.
(see G10 L10 for details)

G10 L11 Pn - Set offset(s) so current position w/ fixture 9 becomes a value.
(see G10 L11 for details)

2. Tool Table

The Tool Table is a text file that contains information about each
tool. The file is located in the same directory as your configuration
and is called tool.tbl. The tools might be in a tool changer or just
changed manually. The file can be edited with a text editor or be
updated using G10 L1. See the Lathe Tool Table
Section for an example of the lathe tool table format.
The maximum number of entries in the tool table is 56.
The maximum tool and pocket number is 99999.

The Tool Editor or a text editor can be used to edit the
tool table. If you use a text editor make sure you reload the tool table in
the GUI.

2.1. Tool Table Format

Table 1. Tool Table Format

T#

P#

X

Y

Z

A

B

C

U

V

W

Dia

FA

BA

Ori

Rem

;

(no data after opening semicolon)

T1

P17

X0

Y0

Z0

A0

B0

C0

U0

V0

W0

D0

I0

J0

Q0

;rem

T2

P5

X0

Y0

Z0

A0

B0

C0

U0

V0

W0

D0

I0

J0

Q0

;rem

T3

P12

X0

Y0

Z0

A0

B0

C0

U0

V0

W0

D0

I0

J0

Q0

;rem

In general, the new tool table line format is:

; - opening semicolon, no data

T - tool number, 0-99999 (tool numbers must be unique)

P - pocket number, 1-99999 (pocket numbers must be unique)

X..W - tool offset on specified axis - floating-point

D - tool diameter - floating-point, absolute value

I - front angle (lathe only) - floating-point

J - back angle (lathe only) - floating-point

Q - tool orientation (lathe only) - integer, 0-9

; - beginning of comment or remark - text

The file consists of one opening semicolon on the first line,
followed by up to a maximum of 56 tool entries.

Note

Although tool numbers up to 99999 are allowed, the number of entries in the
tool table, at the moment, is still limited to a maximum of 56 tools for
technical reasons. The LinuxCNC developers plan to remove that limitation
eventually. If you have a very large tool changer, please be patient.

Earlier versions of LinuxCNC had two different tool table formats for
mills and lathes, but since the 2.4.x release, one tool table format
is used for all machines. Just ignore the parts of the tool table
that don’t pertain to your machine, or which you don’t need to use.

Each line of the tool table file after the opening semicolon contains
the data for one tool. One line may contain as many as 16 entries,
but will likely contain much fewer.

The units used for the length, diameter, etc., are in machine units.

You will probably want to keep the tool entries in ascending order,
especially if you are going to be using a randomizing tool changer.
Although the tool table does allow for tool numbers in any order.

Each line may have up to 16 entries. The first two entries are required.
The last entry (a remark or comment, preceded by a semicolon) is
optional. It makes reading easier if the entries are arranged in
columns, as shown in the table, but the only format requirement is
that there be at least one space or tab after each of the entries on
a line and a newline character at the end of each entry.

The meanings of the entries and the type of data to be put in each are
as follows.

Tool Number (required)

The T column contains the number (unsigned integer) which
represents a code number for the tool. The user may use any code for
any tool, as long as the codes are unsigned integers.

Pocket Number (required)

The P column contains the number (unsigned integer) which
represents the pocket number (slot number) of the tool changer slot
where the tool can be found. The entries in this column must all be
different.

The pocket numbers will typically start at 1 and go up to the highest
available pocket on your tool changer. But not all tool changers follow
this pattern. Your pocket numbers will be determined by the numbers
that your tool changer uses to refer to the pockets. So all this is to
say that the pocket numbers you use will be determined by the numbering
scheme used in your tool changer, and the pocket numbers you use must
make sense on your machine.

Data Offset Numbers (optional)

The Data Offset columns (XYZABCUVW) contain real numbers which
represent tool offsets in each axis. This number will be used if tool
length offsets are being used and this tool is selected.
These numbers can be positive, zero, or negative, and are in fact
completely optional. Although you will probably want to make at least
one entry here, otherwise there would be little point in making an
entry in the tool table to begin with.

In a typical mill, you probably want an entry for Z (tool length
offset). In a typical lathe, you probably want an entry for X
(X tool offset) and Z (Z tool offset). In a typical mill using
cutter diameter compensation (cutter comp), you probably also want
to add an entry for D (cutter diameter). In a typical lathe using
tool nose diameter compensation (tool comp), you probably also want
to add an entry for D (tool nose diameter).

A lathe also requires some additional information to describe the shape and
orientation of the tool. So you probably want to have entries for I (tool
front angle) and J (tool back angle). You probably also want an entry for Q
(tool orientation).

The Diameter column contains a real number. This number is used only
if cutter compensation is turned on using this tool. If the
programmed path during compensation is the edge of the material being
cut, this should be a positive real number representing the measured
diameter of the tool. If the programmed path during compensation is the
path of a tool whose diameter is nominal, this should be a small number
(positive or negative, but near zero) representing only the difference
between the measured diameter of the tool and the nominal diameter.
If cutter compensation is not used with a tool, it does not
matter what number is in this column.

The Comment column may optionally be used to describe the tool. Any
type of description is OK. This column is for the benefit of human
readers only. The comment must be preceded by a semicolon.

2.2. Tool Changers

LinuxCNC supports three types of tool changers: manual, random location
and fixed location. Information about configuring a LinuxCNC tool changer
is in the EMCIO Section of the INI chapter.

Manual Tool Changer

Manual tool changer (you change the tool by hand) is treated like a
fixed location tool changer and the P number is ignored. Using the
manual tool changer only makes sense if you have tool holders that
remain with the tool (Cat, NMTB, Kwik Switch etc.) when changed thus
preserving the location of the tool to the spindle. Machines with R-8
or router collet type tool holders do not preserve the location of the
tool and the manual tool changer should not be used.

Fixed Location Tool Changers

Fixed location tool changers always return the tools to a
fixed position in the tool changer. This would also include
designs like lathe turrets. When LinuxCNC is configured for a fixed
location tool changer the P number is ignored (but read, preserved
and rewritten) by LinuxCNC, so you can use P for any bookkeeping number you
want.

Random Location Tool Changers

Random location tool changers swap the tool in the spindle with the
one in the changer. With this type of tool changer the tool will
always be in a different pocket after a tool change. When a tool is
changed LinuxCNC rewrites the pocket number to keep track of where the tools
are. T can be any number but P must be a number that makes sense for
the machine.

3. Cutter Compensation

Cutter Compensation allows the programmer to program the tool
path without knowing the exact tool diameter. The only caveat is the
programmer must program the lead in move to be at least as long as the
largest tool radius that might be used.

There are two possible paths the cutter can take while cutter
compensation is on to the left or right side of a line when facing the
direction of cutter motion from behind the cutter. To visualize this
imagine you were standing on the part walking behind the tool as it
progresses across the part. G41 is your left side of the line and G42
is the right side of the line.

The end point of each move depends on the next move. If the next move
creates an outside corner the move will be to the end point of the
compensated cut line. If the next move creates in an inside corner the
move will stop short so to not gouge the part. The following figure
shows how the compensated move will stop at different points depending
on the next move.

Figure 2. Compensation End Point

3.1. Overview

Tool Table

Cutter compensation uses the data from the tool table to
determine the offset needed. The data can be set at run time with G10
L1.

Programming Entry Moves

Any move that is long enough to perform the compensation will work as
the entry move. The minimum length is the cutter radius. This can be a
rapid move above the work piece. If several rapid moves are issued
after a G41/42 only the last one will move the tool to the compensated
position.

In the following figure you can see that the entry move is compensated
to the right of the line. This puts the center of the tool to the right
of X0 in this case. If you were to program a profile and the end is at
X0 the resulting profile would leave a bump due to the offset of the
entry move.

Figure 3. Entry Move

Z Motion

Z axis motion may take place while the contour is being followed in
the XY plane. Portions of the contour may be skipped by retracting the
Z axis above the part and by extending the Z-axis at the next start
point.